docs: def get_true_latitude_variables(nc):
      '''
      Returns a list of variables defining true latitude.
  
      CF Chapter 4 refers to latitude as a coordinate variable that can also be
      used in non-standard coordinate systems like rotated pole and other
      projections. Chapter 5 refers to a concept of true latitude where the
      variabe defines latitude in a standard projection.
  
      True latitude, for lack of a better definition, is simply latitude where
      the standard_name is latitude or the units are degrees_north.
  
      :param netCDF4.Dataset nc: An open netCDF dataset
      '''
      lats = get_latitude_variables(nc)
      true_lats = []
      for lat in lats:
          standard_name = getattr(nc.variables[lat], "standard_name", None)
          units = getattr(nc.variables[lat], "units", None)
          if standard_name == 'latitude':
              true_lats.append(lat)
          elif isinstance(units, basestring) and units.lower() in VALID_LAT_UNITS:
              true_lats.append(lat)
      return true_lats